342 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



segment ; ]Aeon composed apparently of four segments, of which the 

 last two are consolidated in the dorsal region ; operculum with a single 

 apical plate. 



The species to which I jiropoae to limit the name Idofea* may be briefly 

 characterized as above, and, of these, the three found on our coast agree 

 further as follows: The body is elongated, its length being from three 

 to four times its breadth, and the sides are nearly parallel. The head is 

 quadrate and not produced at the sides. The eyes are lateral. The 

 antennulffi are small and short, hardly surpassing the third segment of 

 the antennre. The basal segment of the antenme is very short ; the 

 second segment much larger and deeply incised on its under surface ; 

 the third, fourth and fifth segments increase in length but decrease in 

 diameter ; the flageilum is more or less distinctly articulated, the num- 

 ber of articulations increasing with age. The palpus of the maxillipeds 

 is four-jointed, the last segment being composed of two segments united, 

 as is indicated by a notch near the tip. 



The thorax is moderately arched, with the sides but little dilated 

 in the males, somewhat more so in the females. The epimera are con- 

 spicuous and separated from their segments by a suture above, except in 

 the first segment, but may not occux)y its entire lateral margin. The legs 

 differ but little in form throughout, being all more or less perfectly 

 prehensile, but in the first pair only is the carpus triangular. 



The pleon or abdomen appears, when seen from above, to consist of four 

 segments, of which the first two are separated by complete sutures, but 

 the third and fourth by sutiu-es at the sides only. The uropods, forming 

 the abdominal oi)erculum, consist on each side of a flattened, elongated 

 plate, with the anterior end rounded, the sides nearly parallel for most, 

 or all, of its length and bearing at its truncated apex a much shorter 

 more or less tapering or triangular plate. Xeither of these plates is 

 strongly ciliated in our species, but a stout, densely plumose bristle 

 springs from the basal plate, on the inside, near the outer end of the ar- 

 ticulation between the two plates. The stylet on the second pair of pleo- 

 pods of the males is not elongated and may not surpass the lamella to 

 which it is attached. The incubatory pouch is conspicuous in the 

 females. 



Our representatives of this genus may be recognized among the other 

 known Isopoda of the coast by the following characters : The pleon ap- 

 pears to consist of four segments, the first three short and the third 

 united, in the dorsal region, to the large, more or less vaulted, terminal 

 segment ; underneath the pleon is the conspicuous two-valved operculum 

 and, in the antennge, the flageilum consists of several segments. The 

 three species may be distinguished by the form of the tip of the pleon, 

 which is more or less tridentate in I. irrorata (p. 343), pointed in I. 

 phosphorea (p. 347), and truncate in J. robnsta (p. 349). 



* The orthography adopted is that of Fabricius, the author of the genus. 



